I don't know, I think a Loki spin-off movie is definitely a possibility, given his popularity. Only after Thor 3, though.

A Loki one-shot? Even though it'd be tricky to do, I think its almost a sure thing at some point.

Kevin Feige has said recently that Marvel is considering doing more with Loki because of the character's popularity. The publicity tour that Feige did with Tom Hiddleston seems to have opened the head honcho's eyes a bit. He mentioned going to an appearance in South Korea with Hiddleston and being shocked that 7,000 crazed Loki fans turned out to see him. Events like that are shaping Marvel's approach to Loki, according to Feige.

While I am not a huge Loki fan, I think that Marvel would be foolish not to capitalize on his popularity in some way.